Children's coloring markers often contain coloring compositions which are aqueous solutions of dyes commonly known as "acid dyes." The term "acid dye" is somewhat of a misnomer in that it does not describe any particular chemical type of dye, but rather refers to the traditional practice of dyeing fabrics from acidified solutions. These coloring markers have been used by children to write and color on a wide variety of substrates, but primarily on porous surfaces such as, for example, paper. Not all acid dyes are suitable for use in coloring compositions. Generally, only those acid dyes having good chroma, color intensity, and water-solubility are utilized. One drawback of acid dyes, however, is that generally they stain the skin and few are completely washable from children's clothing. Acid dyes also tend to stain many household surfaces.
Coloring compositions often also include such ingredients as humectants, biocides, and surfactants. Humectants function to improve freeze/thaw stability and to control drying out of the marker tip, while biocides serve the obvious function of preventing spoilage in the ink during the expected shelf life of the marker product. To limit a grainy appearance of the ink as it is applied and/or to enhance the flow characteristics of the ink, a small amount of surfactant is ordinarily employed.
A well known deficiency of children's coloring markers is their propensity to leave enduring stains on skin, clothing and other surfaces. While permanence is a desirable characteristic of the so-called "permanent" markers, it is one of the most objectionable properties for coloring instruments used by young children. Accordingly, much effort has been expended over many years by producers of these instruments to reduce or eliminate staining. This is attested by the rather numerous offerings of so-called "washable" markers, which, on close examination, are often found to leave stains on certain substrates, including skin and fabrics typically used in children's clothing. Most such markers achieve their limited washability by utilizing dyes which have good fugitivity from fabrics and by utilizing lowered dye concentrations in an effort to minimize skin staining. In most cases, these "washable" products still leave objectionable stains on the skin. The inks used in such markers therefore lack fugitivity from skin.
In a recent approach, as described in U.S. Pat. No. 5,116,410, an aromatic organic sulfonate is added to enhance the washability of a marker ink composition. However, the colorants utilized in the disclosed compositions are conventional acid dyes.
European Patent Application 0 557 115 discloses a washable dye-containing coloring composition containing a sulfonated phenol-formaldehyde condensation product. The compositions disclosed, however, were directed toward conventional acid dyes.
It is therefore one general object of the invention to provide a method of imparting skin fugitivity to a coloring composition.
Another object is to provide a coloring composition which, in addition to being washable from skin, exhibits enhanced launderability from fabrics and other surfaces.
A related object is to provide non-toxic coloring compositions, such as inks, which are suitable for use by young children who may make marks on themselves and their clothing.
These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent to those skilled in the art from the following description of the invention and the appended claims.